The purpose of this study was to develop a scale to measure the self-image instability of early adolescents. The subjects were 937 students (272 fifth and sixth graders and 665 junior high school students) who responded to a self-report questionnaire twice, one month apart. Factor analysis revealed that the self-image instability scale includes three subscales: positive changes, negative changes, and neutral instabilities. The scale demonstrated good correlations with test–retest and existing scales. Negative self-image changes and neutral instabilities had positive correlation with stress responses, while positive changes had small negative correlations with stress responses.